An organic light emitting diode (OLED) is generally composed of two electrodes (an anode and a cathode) and one or more organic material layers that are disposed between the electrodes. In the organic light emitting diode having this structure, if a voltage is applied between the two electrodes, a hole flows from an anode and an electron flows from a cathode into an organic material layer, they are recombined with each other to form an exciton, and a photon corresponding to an energy difference is emitted while the exciton falls to the base state. By this principle, the organic light emitting diode emits visible rays, and an information display diode or illumination diode may be manufactured by using this.
In the organic light emitting diode, there are a bottom emission type in which light that is generated in the organic material layer is emitted to a substrate and a top emission type in which light is emitted in the opposite direction of the substrate. In a both-side emission type, light is emitted in the substrate direction and in the opposite direction of the substrate.
In the top emission or both-side emission organic light emitting diode, an electrode that is not contacted with the substrate and disposed at the opposite side of the substrate should be transparent at a visible ray region. In the organic light emitting diode, a conductive oxide film such as IZO (indium zinc-oxide) or ITO (indium tin-oxide) is used as the transparent electrode. However, since the conductive oxide film has a very high work function, in the case of when the cathode is formed by using this, it is difficult to inject electrons from the cathode to the organic material layer. Accordingly, operation voltage of the organic light emitting diode is largely increased, and important diode properties such as light emission efficiency and the like are deteriorated. Therefore, there is a demand for manufacturing the top emission or both-side emission organic light emitting diode that has a structure in which the substrate, the cathode, the organic material layer and the transparent anode are sequentially layered, that is, an inverted structure.